Electric motor with minimized cogging and related method of determining stator pole geometry

Abstract

An electric motor with reduced cogging torque and related method of determining a stator pole geometry are disclosed. The electric motor includes a rotor (80, 91, 96) and a stator (50A, 50B, 50C, 50D, 60A, 60B, 60C, 60D, 70A, 90B, 94B, 98) having a stator pole geometry incorporating non-magnetic body segments (110) and magnetic body segments (100) as magnetic reluctance equalizing elements to provide an equalized magnetic body distribution along a circumferential periphery of the stator. The method comprises defining a first group of stator poles skewed at an electric angle of 360 / (2S), defining a second group of stator poles deviated from the first group of stator poles by an electric angle of 180 degrees, and synthesizing the first and second groups of stator poles pieces to provide a stator including a plurality of stator poles defined in the stator pole geometry to have an equalized magnetic flux distribution pattern along a circumferential periphery of the stator.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is related to Japanese Patent Application No. 2005-131813 filed on Apr. 28, 2005, the content of which is hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]1. Technical Field of the Invention[0003]The present invention relates to electric motors and, more particularly, to an electric motor with low cogging torque for use in an automobile and a truck or the like and a method of determining a stator pole geometry for controlling cogging torque in the electric motor.[0004]2. Description of the Related Art[0005]As technologies to reduce cogging torque of electric motors in general practice, skewing technique has been explored to reduce cogging torque. Skewing technique features to form stator poles in a skewed pattern such that a stator has rotational positions deviated along an axial direction of a rotor. With such a structure, the stator poles are deviated at an electric angle of 180 degrees to allow the sta...

AI Technical Summary

Benefits of technology

The present invention provides an electric motor with a stator that has an equalized magnetic body distribution pattern over a circumferential periphery of the stator to minimize cogging torque. The stator poles have magnetic reluctance equalizing means, such as non-magnetic body segments or magnetic body segments, to equalize magnetic reluctance and minimize cogging torque. The use of the magnetic reluctance equalizing means allows for a simplified construction with low-cost components. The stator poles may be skewed at given angles and the magnetic reluctance equalizing elements may include non-magnetic body segments or magnetic body segments. The non-magnetic body segments may include air gaps, which simplifies the fabrication process and reduces cogging torque. The number of stator phases may be an odd number and the stator and rotor may have a total skew angle that lies at an electric angle of substantially 360 / (2S).

Problems solved by technology

However, with the skew angle set at too large a value, a drop occurs in utilization efficiency of a magnetic flux of the rotor, resulting in a decrease in output torque.

In such a case, cogging torque cannot be completely removed.

By the way, with the related art technique of employing added notches as disclosed in the above literature, magnetic reluctances occurring in the air gap segments between the stator cores and the added notches unequally vary with the resultant occurrence of issues wherein the added notches are effective to reduce cogging torque to some extent but have no remarkable effect of completely minimizing cogging torque.

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